The microelectronics industry is dependent upon spin coating for the deposition of uniform thin films on various flat substrates, including silicon wafers for integrated circuits and glass for optoelectronic devices. Spin coating processes typically involve the injection of a liquid coating onto a flat substrate that is rotating at a high rate of speed such as several hundred to several thousand RPM. A spin coater operates by spreading a thin liquid layer (liquid coating solution) on a substrate using the centrifugal force of a spinning substrate. The spreading liquid layer then forms a fairly uniform film after evaporation that covers up and planarizes topological unevenness leaving pin-hole free films. The liquid coating solution is typically comprised of a material that has low volatility such as a polymeric material or an oligomer. These low volatile materials are then dissolved in a volatile liquid solvent or liquid solvent mixture. The volatile liquid solvents are typically volatile organic solvents (VOC), chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC), and perfluorocarbons or mixtures thereof such as methyl ethyl ketone (MEK), ethyl acetate, chloroform, toluene, isoamyl acetate, Freon-113, Freon-22, Freon-134a, Freon-227, perfluoromorpholine, etc. The liquid coating solution then thins in a fairly uniform matter across the spinning flat substrate and the excess liquid coating solution falls off the edge of the substrate and is collected. The thin film of liquid coating solution that is retained on the rotating flat substrate continues to evaporate leaving behind a uniform thin film of the compound that has low volatility. The film typically is comprised of a polymeric material (such as a photoresist, interlayer dielectric) but other materials can also be deposited in this way such as low molecular weight compounds (adhesion promoters, antireflective coatings) or sol-gel precursors.
Sometimes a spin coating apparatus is used to remove a substance from a substrate. For example, to develop an exposed photoresist pattern, a liquid solvent is injected onto a substrate that is or will be rotating at a high rate of speed. This liquid solvent can then dissolve the desired substance off the rotating substrate effectively removing the substance off of the rotating substrate.
Spin coating is a solvent intensive process and accounts for a large portion of the use of solvents by the microelectronics industry. Accordingly, there remains a need for spin coating methods and apparatus that reduce or eliminate the use of VOC, CFC, HCFC, HFC, or PFC solvents.